This invention relates to improved apparatus and techniques for monitoring the concentration of combustibles in a combustible fuel environment.
A combustible element analyzer monitors either the input or output from a combustion source and determines the percentage concentration of combustible elements in that sampling. To achieve this monitoring, a sample of the combustion process is obtained from a furnace or other source and forced past a combustion element analyzer, which forms the present invention.
Monitoring combustion element concentration provides information that aids in achieving combustion efficiency In the typical combustion process, an oxidation reaction occurs between oxygen (O.sub.2) and an element or substance which readily combines with oxygen in an exothermic reaction. The end result, of course, is to obtain heat from this reaction and utilize that heat directly or transform it into other means of useful energy, and to measure the energy. The typical combustion reaction follows a well-defined stoichiometric relationship between the elements involved. If the concentration of the combustible element is higher that optimum level in the combustion chamber, the combustible element tends to retard the reaction. If the concentration of combustible element becomes too high, the oxidation may be extinguished. If, on the other hand, the combustible concentration is too low (that is, the oxygen is in too high a concentration) the combustion will go to completion but the energy given off in the form of heat tends to heat the excess air rather than be useful to the system. It has been found that by monitoring the reactions of the combustion process, it is possible to determine whether the combustion reaction is efficiently producing heat, or if steps need be taken to increase efficiency.
Another use for the combustible monitoring technique is to monitor pollutants. Since many pollutants are actually inefficiently burned combustibles, the combustible sensor can be utilized to determine whether changes need be made in an oxidation reaction process. The system therefore can be used to monitor automobile exhaust systems, industrial exhaust systems, and any other source of combustion products.
A presently available combustible sensor known as the Taguchi sensor or TGS, employs a solid-state device made of a sintered N-type metallic oxide produced from the iron, zinc and tin families. A heater coil is embedded in the oxide to bring the metallic oxide semiconductor device to operating temperature in the 150.degree.-300.degree. C. range. At this temperature, a functional relationship exists between the conductivity measured in the metallic heater coils and the combustible gas concentration in the sample. Utilization of this functional relationship allows determination of the combustible gas concentration.
The TGS sensor, however, involves serious shortcomings which the present invention adequately overcomes. The TGS apparatus is not intended for continuous accurate measurement of combustible gases, but rather it is utilized to trigger an alarm whenever a dangerous level of combustible gases exists. Since the heater coil is not only used to measure the combustible gas concentration but also is used to heat the element, signal drift becomes a major problem in the apparatus. The apparatus is further susceptible to interference from gases such as nitric oxide, sulphur dioxide, or water vapor, which can alter the results obtained.